The present invention relates to a method and an apparatus for sensing an air flow into a cylinder of an internal combustion engine, and more particularly to a method and an apparatus for controlling fuel consumed in the internal combustion engine arranged to use the method for sensing the air flow into the cylinder.
It is known that the flow of air into an intake passage of the internal combustion engine does not completely coincide with the flow of air actually sucked into the cylinder. To accurately adjust an air/fuel ratio, the flow rate of the fuel to be fed to the internal combustion engine is required to be defined on the amount of air actually flown into the cylinder.
There has been known such a technique as preparing a two-dimensional map of correction values in a lot of operation areas defined by the parameter of engine speed and the negative pressure inside of the intake manifold, correcting a charging efficiency of an intake flow rate in each operation area with reference to the corrections read from the map, and determining a basic fuel injection amount based on the corrected intake air flow.
For example, the invention disclosed in Japanese Patent Application un-examined publication No. JP-A-58-41230 issued on Mar. 10, 1983 has proposed a technique arranged to determine the intake air flow on the basis of engine speed and the negative pressure of the intake pipe and, and then determine the fuel injection amount according to the value of intake air flow. The technique also has a step of correcting a volumetric efficiency of the engine based on a product of a correction value according to the intake negative pressure and a correction value according to the engine speed.
In addition, the invention disclosed in Japanese Patent Application un-examined publication No. JP-A-5-240104 issued on Sep. 17, 1993 has proposed a method for deriving an air flow into the cylinder based on the presumed value of the intake pipe pressure and engine speed.
However, the conventional fuel injection apparatus of the internal combustion engine disadvantageously needs a large storage capacity of a memory, because the corrections of the volumetric efficiency of the engine are required to be stored with respect to the axes of the negative pressure values and the engine speed values. Further, the prior art has another disadvantage that no consideration is taken about an adverse effect of an error resulting from a rebound of an output value of an air flow meter. This adverse effect takes place when the pressure of the intake pipe comes closer to the atmospheric pressure. This is because the pressure of the intake pipe is presumed from the intake air flow of the internal combustion engine sensed by a thermal type air flow meter. Hence, the prior art does not derive a precise air flow into the cylinder.
Further, that prior art uses an interpolation method for obtaining the correction values of the operation not shown in the map from the correction values of the operation area indicated in the map. In this case, the operation areas derived between two different operation areas appear as discontinuous areas. This indicates that the correction value derived by the interpolation may be erroneous.